[The complete band4.2 deficiency in human red cells].

The complete band4.2 deficiency with a point mutation (GCT-->ACT at codon142: Nippon type) in red cell membrane protein4.2 gene is specific for the Japanese population. The biochemical properties of band4.2 protein have been studied extensively. However, the physiolosical functions of this protein in situ have been unknown. Therefore, we tried to clarify the physiological role of band4.2 by biochemical, biophysical and electron microscopic studies in the patient with the Nippon type mutation. Band4.2 deficient red cells demonstrated significant abnormalities in the function of both the cytoskeletal network and band3 protein, as summarized in our results. 1 Deformability of red cell membrane was decreased when heat-treated up to 48 degrees C. 2 Under the these conditions, the cytoskeletal network became markedly disrupted, and the number of intramembrane particles was reduced with a shift to larger sizes, indicating the possibility of increased oligomerization of band3 molecules in the red cells. 3 The lateral and rotational mobility of band3 in the red cells was substantially increased. 4 Band4.2 protein was found to bind to spectrin in solution and to promote the binding of spectrin to ankyrin-stripped inside-out vesicles. These results indicate the possibility that band4.2 may play a role in connecting the cytoskeletal network to band3 protein as a kind of anchoring protein.